Not applicable.
Not applicable.
1. Field of Invention
This invention relates to a system of hoisting blocks for heavy cranes and hoisting devices. Specifically, the invention describes a system of load blocks connected in series to enable heavy lifts to be conducted with standard/conventional winch drums and hoist lines that by conventional rigging, would not be able to provide the capabilities of combined lift capacity and hoisting height.
2. Related Art
The art of rigging and developing mechanical lifting advantage using pulleys has long been known. The development of heavy capacity cranes, however, has changed the load demands on load lines and reeved systems. Heavy capacity cranes have the mechanical and structural ability to lift heavy loads, but the strength of the load line, the winches"" maximum line pull and the capacity of the drums to hold sufficient wire rope are often limiting factors. In addition, load blocks reeved for heavy lifts are restrictive in hoisting speed, and those reeved for speed for lift are limited in lift capacity. One way to overcome these limitations is the use of oversized high strength wire rope. The use of oversized wire rope poses operational problems. Since it is thicker and heavier than conventional wire rope, high strength wire rope requires large capacity hoisting drums and sheaves for adequate wrapping, is difficult to handle during set-up and rigging due to its weight and inflexibility, may require special linear winches, and is more expensive than conventional wire rope.
The typical alternative to the use of oversized wire rope by heavy cranes is the use of multiple part reeving, which uses standard strength wire rope. Multiple part reeving distributes the weight of the load over multiple parts of the wire rope. Heavy capacity cranes typically use double load lines operating in parallel, each line having a dedicated set of boom and load block sheaves forming distinct reeving systems.
Heavy capacity cranes typically have long booms, to be able to lift tall objects, have a long horizontal reach, and/or have a high vertical reach. Boom lengths over 300 meters are becoming more common. If standard wire rope is used, the long boom length of the high capacity crane, combined with the reeving requirements to support a heavy load, require long lengths of standard load line. The amount of line required is at least the length of the boom plus that length multiplied by the number of parts in the multiple reeving. Thus, a boom with a 100-meter boom and an eight part reeving from each drum requires a total of 900 meters of wire rope for each load line. Spooling this length of line requires special handling equipment for the wire rope, including a large capacity hoist drum. It would be a new and useful improvement over the prior art for a hoisting system be capable of using standard wire rope and standard size hoist drums in a high capacity crane. It is understood that there are many sizes of wire rope and hoist drums. However, the term xe2x80x9cstandardxe2x80x9d is nonetheless used to denote sizes that are economical and are not oversized. Also, the words xe2x80x9cwinch drumxe2x80x9d are used herein to describe a mechanical means of applying a tensile (pulling) force to a wire rope or other flexible tensile load support mechanism, and is intended to cover other means of applying the pulling force, such as a linear winch, hydraulic jacks and so forth.
Accordingly, the objectives of this invention are to provide, inter alia, a new and improved load block system for heavy cranes and lifting devices that:
uses standard size (i.e. economical sized) wire rope for the load line;
uses standard size (i.e. economical sized) hoisting drums;
uses standard boom sheaves and load block sheaves;
enables light capacity with high hoist speed and heavy capacity with low hoist speeds all with the one reeving arrangement;
enables large capacity lifts on long boom lengths with hoisting equipment that was previously designed for shorter boom lengths only; and
is interchangeable between cranes.
These objectives are addressed by the structure and use of the inventive multiple load block system. Multiple load block sheaves are vertically oriented in series, each forming distinct sets of reeving lines between lower load block sheaves and upper sheaves or attachment points. This orientation only requires each set of sheaves to move vertically through a proportional percentage of the total vertical height of the boom tip. The use of multiple load blocks vertically oriented in series allows the use of standard sized winch drums, since each set of reeving lines must only traverse a portion of the total travel distance of the load hook. If the number of parts of line in the reeving lines is different, then the different reeving line sections afford different travel speeds. In addition, both high capacity lifts at slow speeds and lower capacity lifts at higher speeds can be effected by the use of this system. As an example, consider a two part reeved system in series with the top set of reeving being reeved for heavy lifts (many parts of line) and the lower set of reeving being reeved for light lifts (few parts of line). When light lifting duties are required, the bottom set of reeving will be run up and down at a resulting high speed, providing a good cycle time. When a heavy lift is required, first the lower and middle set of blocks will be lowered down to the ground, then interconnecting steel link plates will be connected between the lower and middle blocks, effectively bypassing the lower system (and removing the weak link) and then the upper system of reeving will be used for the heavy lift.
Other objects of the invention will become apparent from time to time throughout the specification hereinafter disclosed.